Rudbäck first studied the essential oils sweet orange and petitgrain, which containe some of the most common fragrance terpenes. It has previously been shown that exposing some common fragrance compounds to air leads to the formation of potent allergens, hydroperoxides in particular.

The hydroperoxides from the fragrance compounds are generally difficult to identify and quantify. They are unstable, lack UV absorbance, are similar and come in several different forms. In addition, they are found in low concentrations in complex mixtures. Rudbäck identified these hydroperoxides by separating them using either liquid or gas chromatography and detecting them with mass spectrometry. Liquid chromatography was used for low detection limits, while a high peak capacity was obtained with gas chromatography.

Rudbäck showed that hydroperoxides from the fragrance compounds were present already before the bottles were opened, and the levels increased when the oils were exposed to air. The study shows that the oils didn’t have any natural protection against the formation of allergenic compounds.

To learn more about what happens when exposing fragrance compounds to air, Rudbäck studied two monoterpenes, alpha-terpinene (tea tree oil) and citronellol (geranium). She found that the allergenic effect of both compounds increased tenfold after air exposure compared to the pure fragrance compounds.